Transcript posterior pituitary

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EXAM ON WED
1/3 Fill in the Blank
1/5 definitions
1/5 short answer
Few true and false
1/3 Essay or Critical Thinking
QUESTIONS??
pituitary gland is Master Gland
anterior pituitary
(adenohypophysis)
classical gland composed
predominantly of cells that secrete
protein hormones.
posterior pituitary
(neurohypophysis) -not really an
organ, but an extension of the
hypothalamus. composed largely of
the axons of hypothalamic neurons
which extend downward as a large
bundle behind the anterior pituitary.
It also forms the so-called
pituitary stalk, which appears to
suspend the anterior gland from the
hypothalamus.
Hormones of the Pituitary
pituitary gland - pea-sized structure located
at the base of the brain.
In humans, it consists of two lobes:
Anterior Lobe
Posterior Lobe
The Anterior Lobe
The anterior lobe contains 6 types of secretory
cells, all but one of which are specialized to
secrete only one of the anterior lobe hormones.
All of them secrete their hormone in response to
hormones reaching them from the hypothalamus
of the brain
Thyroid Stimulating Hormone (TSH)
TSH (also known as thyrotropin) –
glycoportein consisting of:
a b chain of 112 amino acids and
an a chain of 89 amino acids.
The a chain is identical to that found in
two other pituitary hormones, FSH and
LH as well as in the hormone chorionic
gonadotropin.
The secretion of TSH is
-stimulated by the arrival of thyrotropin releasing
hormone (TRH) from the hypothalamus.
-inhibited by the arrival of somatostatin from the
hypothalamus.
As name suggests, TSH stimulates the thyroid
gland to secrete its hormone thyroxine (T4). It
does this by binding to GPCRs on the surface of
the cells of the thyroid.
.
Some people develop antibodies against their own
TSH receptors. When these bind the receptors,
they "fool" the cell into making more T4 causing
hyperthyroidism. The condition is called
thyrotoxicosis or Graves' disease.
A deficiency of TSH causes hypothyroidism: inadequate
levels of T4 (and thus of T3 ).
Recombinant human TSH has recently become available
to treat patients with TSH deficiency.
Some people inherit mutant TSH receptors. This can
result in hypothyroidism.
A deficiency of TSH, or mutant TSH receptors, have also
been implicated as a cause of osteoporosis. Mice, whose
TSH receptors have been knocked out, develop increased
numbers of bone-reabsorbing osteoclasts.
Follicle-Stimulating Hormone (FSH)
FSH is a heterodimeric glycoprotien
consisting of
- same a chain found in TSH (and LH)
- b chain of 115 amino acids (gives it its
unique properties)
Synthesis and release of FSH is triggered by
the arrival from the hypothalamus of
gonadotropin releasing hormone GnRH
Effect of FSH depends on one's sex
FSH in females
In sexually-mature females, FSH (assisted by LH)
acts on the follicle to stimulate it to release
estrogens
FSH in males
In sexually-mature males, FSH acts on
spermatogonia (with the aid of testosterone)
stimulating the production of sperm.
Luteinizing Hormone (LH)
LH is synthesized within the same pituitary cells
as FSH and under the same stimulus (GnRH).
Heterodimeric glycoprotein
-same 89 aa a subunit found in FSH & TSH
- b chain of 115 aa that is responsible for its
properties.
Effects of LH also depend on sex
LH in females
In sexually-mature females, LH
stimulates the follicle to secrete estrogen in the
first ½ of the menstrual cycle
a surge of LH triggers the completion of meiosis I
of the egg and its release (ovulation) in the middle
of the cycle
stimulates the now-empty follicle to develop into
the corpus luteum, which secretes progesterone
during the latter ½ of the menstrual cycle.
LH in males
LH acts on the interstitial cells (also known as
Leydig cells) of the testes stimulating them to
synthesize and secrete the male sex hormone,
testosterone.
LH in males is also known as interstitial cell
stimulating hormone (ICSH).
Prolactin (PRL)
198 aa
During pregnancy it helps in the preparation of
the breasts for future milk production.
After birth- promotes the synthesis of milk.
Prolactin secretion is
stimulated by TRH
repressed by estrogens and dopamine
In pregnant mice, prolactin stimulates the growth
of new neurons in the olfactory center of the of
the brain.
Growth Hormone (GH)
also called somatotropin
191 aa
GH-secreting cells are stimulated to synthesize
and release GH by the intermittent arrival of
growth hormone releasing hormone (GHRH)
from the hypothalamus.
GH promotes body growth by:
binding to receptors on the surface of liver cells
this stimulates them to release insulin-like growth
factor-1 (IGF-1; also known as somatomedin)
IGF-1 acts directly on the ends of the long bones
promoting their growth
Things that can go wrong
In childhood-hyposecretion of GH produces
the stunted (but normally well-proportioned)
growth of a midget.
Growth retardation can also result from an
inability to respond to GH. This can result
from inheriting mutant genes encoding the
receptors for GHRH or GH or a defect in
STAT 5B.
Hypersecretion leads to gigantism
In adults, a hypersecretion of GH leads to
acromegaly.
Hormone-replacement therapy
GH from domestic mammals like cows and pigs
does not work in humans. So for many years, the
only source of GH for therapy was that extracted
from the glands of human cadavers. This supply
was shut off when several patients died from a
rare neurological disease attributed to
contaminated glands.
Now, with recombinant DNA methods,
recombinant human GH (rHGH) is available.
While a great benefit to patients suffering from GH
deficiency, there has also been pressure to use it to
stimulate growth in youngsters who have no
deficiency but whose parents want them to grow up
tall. Summer of 2003, the U.S. FDA approved the
use of human growth hormone (HGH) for
boys predicted to grow no taller than 5′3″ and
for girls, 4′11″
even though otherwise perfectly healthy.
ACTH — the adrenocorticotropic hormone
ACTH of 39 aa peptide.
Produced from a larger precursor
proopiomelanocortin (POMC).
ACTH acts on the cells of the adrental cortex
stimulating them to produce
glucocortiocoids, like cortisol
mineralcortiocoids, like aldosterone
Androgens (male sex hormones, like testosterone
in the fetus, ACTH stimulates the adrenal cortex
to synthesize a precursor of estrogen called
dehydroepiandrosterone sulfate (DHEA-S) which
helps prepare the mother for giving birth
Production of ACTH depends on the intermittent
arrival of corticotropin-releasing hormone (CRH)
from the hypothalamus.
Hypersecretion of ACTH is a frequent cause of
Cushing's disease.
Alpha Melanocyte-Stimulating Hormone (αMSH)
another cleavage product POMC
In fact, α-MSH is identical to the first 13
amino acids at the amino terminal of
ACTH.
Pituitary cell types of Rathke's pouch
Corticotropes, produce (POMC) and
cleave it into adrenocorticotropic hormone
(ACTH) needed for glucocorticoid synthesis
in the adrenal gland
Melanotropes, which produce POMC, but
cleave it into αMSH (for pigment formation,
feeding regulation)
Somatotropes, which produce growth
hormone
Pituitary cell types of Rathke's pouch
Lactotropes, which make prolactin (for
milk production, uterine contractions)
Gonadotropes, which synthesize
lutenizing hormone and follicle
stimulating hormone (for gonad growth
and development)
Anterior pituitary cells
Somatotropes
Lactotropes
Thyrotropes
Gonadotropes
Corticotropes
Intermediate pituitary cell, secreting melanocyte-stimulating hormone
Magnocellular neurosecretory cells
secreting oxytocin
secreting vasopressin
The Posterior Lobe
The posterior lobe of the pituitary releases 2
hormones, both synthesized in the hypothalamus,
into the circulation.
Antidiuretic Hormone (ADH).
ADH is a peptide of 9 amino acids. It is also
known as arginine vasopressin. ADH acts on the
collecting ducts of the kidney to facilitate the
reabsorption of water into the blood. This it acts
to reduce the volume of urine formed (giving it its
name of antidiuretic hormone).
A deficiency of ADH or
inheritance of mutant genes for its
receptor (called V2)
leads to excessive loss of urine, a condition
known as diabetes insipidus. The most
severely-afflicted patients may urinate as
much as 30 liters (almost 8 gallons!) of urine
each day. The disease is accompanied by
terrible thirst, and patients must
continually drink water to avoid dangerous
dehydration.
Oxytocin
peptide of 9 aa
Acts on certain smooth muscles:
stimulating contractions of the uterus at the time
of birth
stimulating release of milk when the baby begins
to suckle.
Oxytocin is often given to prospective mothers to
hasten birth.
Oxytocin also acts in the brain where it enhances:
bonding between males and females after they
have mated;
bonding between a mother and her newborn;
and, in humans, increases the level of one's trust
in other people.
Hormone
Major target organ
Major Physiologic effect
Anterior
GH Liver, adipose tissue
Promotes growth (indirectly) and control of protein, lipid and
carbohydrate metabolism
TSH Thyroid gland Stimulates secretion of thyroid hormones
ACTH Adrenal gland (cortex)
Stimulates secretion of glucocorticoids
PRL Mammary gland
Milk production
LH Ovary and testis
Control of reproductive function
FSH Ovary and testis
Control of reproductive function
Hormone
Major target organ
Major Physiologic effect
Posterior
ADH Kidney
Conservation of body water
OXY Ovary and testis
Stimulates milk ejection and uterine contractions
REVIEW of Pituitary Gland
"master" gland of the endocrine system because
it controls the functions of the other endocrine
glands.
attached to the hypothalumus by nerve fibers.
the anterior lobe
the intermediate lobe
the posterior lobe
Each lobe of the pituitary gland produces certain
hormones.
anterior lobe:
GH
PRL
ACTH
TSH
FSH
LH
intermediate lobe:
melanocyte-stimulating hormone
posterior lobe:
ADH and oxytocin
Figure 4. Detail from the
fresco, "Creation of
Adam," by
Michelangelo
- visible on the ceiling of
the Sistine Chapel
in the Vatican in Rome,
painted 1508-1512.
Photograph of the fresco
showing God giving
spiritual life and
intellect to Adam through
his touch;(B) The
contour of the same
image is
reminiscent of a midline
saggital section of the
brain and includes the
hypothalamus,
pituitary and
brainstem.